Generally, agricultural harvesting machines, such as forage or combine harvesters, are equipped with crop collecting devices, such as corn or grain headers or pick-up units, for collecting crop material from the field and deliver it to further crop processing means of the harvesting machine. In a forage harvester, for example, these devices usually comprise a set of feed rolls, a rotating cutterhead cooperating with a fixed shear bar, operable to comminute the crop material fed thereto by the feed rolls, and a blower, which receives the comminuted material and propels it out of the harvester through a spout, directing the material flow into a container moved behind or aside the forage harvester. The crop processing means of a combine harvester customarily comprise a straw conveyor, which feeds the crop material to threshing means, including one or more threshing drums, further separation means, such as straw walkers, and cleaning means, including sieves and a ventilator, operable to remove impurities such as chaff and pieces of straw from the grain kernels.
During normal harvesting operation, these conveying and harvesting devices demand a large amount of power from the harvester's engine and are most advantageously linked thereto by mechanical drivelines. In some case however, it may be required to reverse one or more of these devices. This usually is done by breaking the drive line from the engine and branching a reversing motor to the one or more devices. When the harvester returns to normal harvesting operation, the reversing motor is inactivated and has no further functions.
A hydraulic reversing system for the cutterhead of a forage harvester is illustrated in Eurpean Patent Application No. 0.335.332. During the knife sharpening operation, the cutterhead rotation is reversed by means of a hydraulic motor in order to provide the knife edges with an optimum cutting profile. A clutch mechanism has to be energized before the driving power from the motor is transferred upon the cutterhead. During normal harvesting operation, the hydraulic motor is shut off and no more use is made thereof.
A hydraulic reversing system for the header and the straw elevator of a combine harvester is illustrated in European Patent Application No. 0.180.027. When the auger of a grain header or the straw elevator gets blocked by an excessive amount of crop material, the operator can reverse the header and the straw elevator in order to remove the obstruction from the harvester. The drive line from the engine to the straw elevator is broken and a hydraulic motor is branched to the drive line of the header and the elevator by means of a hydraulically operated clutch mechanism. When the hydraulic motor is deactivated in order to return to normal working conditions and the oil pressure has dropped consequently in the clutch circuit, the clutch mechanism disengages and no more use is made of the reversing motor.